Stapling mechanism



STAPLING MECHANISM Filed May 19, 1934 4 Sheets-Sheet 1 A a n I I I I l I I I .uvua-av vv. uau. 20

A, INVENTOR 8 5% & BM,

Feb. 22, 1938. H. J. SPENCER vSTAPLIING MECHANISM Filed May 19, 1954 4 Sheets-Sheet 2 Feb. 22, 1938. J SPENCER 2,109,203

STAPLING MECHANISM Filed-May 19, 1934 4 Sheets-Sheet 5 M M Q DXXBM mm. 4 fllllllll- H. J. SPENCER STAPLING MECHANISM Fiid May 19, 1934 Feb. 22, 1938.

INVENTOR Patented Feb. 22, less v 2,109,203

uuirsnsrArss *eATsNT i 2.10am s-rnrusc MECHANISM Herman I. Spencer, West vie Pa. Application May 1, 1934, .Serial No. 126,565

as Claims. (01. 1-49) This invention relates to stapling mechanism, Fig. 19 is a vertical longitudinal section and more'particularly to a mechanism for driV- through the stapling mechanism shown in Fig. 6

ing wide staples. but showing the plunger in the act of being raised In the accompanying drawings which iliusor retracted. trate my invention, p The mechanism operates in general by the 5 Fig. 1 is a view principally in central vertical compression of a spring during the retracting of section oi one embodiment of my invention; the plunger away from the work, the force of the Fig. 2 is a view in end elevation of the mecha- I spring when released lmpeiling the plunger nism shown in Fig. 1; against a staple and driving the latter into the Fig. 3 is a perspective view of the plunger; object which is to receive it. 10

Fig. 4 is a side view, principally in elevation, of As illustrated in Figs. 1, 4 and 5, the mechathe mechanism shown in Fig. 1, the lever being nism includes a plunger assembly (indicated in in partly lowered position and the plunger on general by the numeral 2) and a base assembly the point of being released for its drivlng'stroke, (indicated in general by the numeral 3), the latthe housing being partially broken away to illuster including means I for feeding staples. These 15 trate the feed of the staples; two assemblies have telescoping parts providing Fig. 5 is an exploded view of the mechanism a slldable mounting of one on the other, the purof Fig. 1, the base assembly being partially sepapose being to permit ready attachment and derated from the plunger assembly by partial withtachment of the assemblies. More particularly, 'drawal cf lugs of the plunger assembly from teleas illustrated in Figs. 5 and 9, the plunger asscopic engagement with parts on the housing of sembly includes a plunger housing 5 whose bed the feeding means; plate 8 has projections i, one at each side. On Fig. 6 is a perspective view of a mechanism for top of the housing 9 for the staple feeding means driving narrower staples using a driving plunger 4 is fixed the apron i0. At each side of the apron similar to the one shown in Figs. 1 and 7 but acis a telescopic holder or pocket l2 for slidably retuated by but a single spring; ceiving a projection or lug I. As indicated in Fig. 7 is a sectional view through one of the Figs. 10 and 11 the apron Ill may be secured in springs and spring housings of the plunger of registering position on top of the housing 9 by Fig. 3, being taken on line VII-VII; lugs it struck from the plate from which the Fig. 8 is a perspective view of a spring stool; apron is made, these lugs being received in open- 30 Fig. 9 is a perspective view of the plunger ings M in the in-turned flanges l5 of the houshousing; ing 9. The edges of the plate of which the apron Fig. 10 is a perspective view of the base as- 40 is made may be bent inwardly, to provide the sembly with the follower removed; pockets i2, this being the construction shown in Fig. 11 is a perspective view of the housing of Figs. 2 and 10. As a preliminary step, P rtions 35 the feeding means; of the edges of the plate are cut out at it so Fig. 12 is a perspective view of the cutter bar; that when these ,edges are inturned, they fit Fig. 13 is a perspective view of the follower around the plunger housing. Screw holes ii are with a fragment of the coil feeder spring atalso provided in these edges so that when the tached thereto; projections l have been received in the sockets 40 Fig. 14 is a perspective view of the yoke l2, screws i9 may be tightened to clamp the two mounting for the feeder spring device; assemblies together.

Fig. 15 is a perspective view of the spring clip The feeding means 4 within the housing 9 inwhich is received in slots in the yoke. cludes a staple guide 20 in the form of a channel Fig. 16 is a sectional view similar to Fig. 7 but having lip-turned flanges 2i. The outer ends of 45 including also the plunger housing and a portion the flanges 2| are deflected slightly toward each of the base-assembly so as to illustrate the parts other as indicated in Figs. 2 and 10 to facilitate when the plunger is just about to be released for loading staples into the feeding means. A rib it driving stroke; 22 extends longitudinally of the channel; and 59 Fig. 17 is a similar view illustrating the parts the tops of the flanges 2| and the rib 22 support during cushioning of the driving stroke; the p s as y are fed 810118 W in the Fig. 18 is a view similar to Fig. 1 showing a housing 9. The flanges i5 overlie the border modification in which an adjustable abutment is p rti s o th stap s so as t ta n t in n provided for varying the extent of upward and as they are fed into operative position bestroke of the plunger. neath the plunger, their accurate positioning is further insured by a depression 23 (see Figs. 1 and 10) in the apron i3.

Just before reaching operative position beneath the plunger the staples pass over a cutter bar 23 which is fixed to down-turned lugs 23 of the bed plate 3 by means of screws 21. Passages 23 are extended through the cutter bar to permit the depending ends of the staples to pass through. The depression 23 in the apron l3 closely overlies the top of the cutter bar 23, so that the staples are positioned closely against the top of the cutter bar as they are fed along.

The staples are urged along the guide 23 by a follower, indicated in general by the numeral 33 (see Fig. 13), which is pulled toward the plunger assembly by the tension of a feeder spring device 3i, later to be described in detail. The ruggedness of the follower preferably depends on the size of the staples. In Fig. 3 is illustrated a fairly light follower which can be employed for small staples without serious difliculty'with deflection of the follower. For wide staples it is unsatisfactory to merely increase the size of the follower, as the light material of which such followers are made is so readily deformed that if a followerof suflicient size to be rigid is used, its length excessively decreases the capacity of the feeding means. On the other hand. the clearance between certain portions of the feeding means is so small that it is not practical to work up a relatively heavy plate into channel-shape for use as a follower. In accordance with my invention, the follower may comprise a channel-shaped member 33 of relatively light thin material with an opening 33 therein. A stiffening plate 33 is secured to the underneath side of the member 33, as by spot welding, with a raised portion 33 let into the opening 33. This opening 33 is wide'enough so that when the follower 33 moves along the guide 23, the longitudinal rib 22 is bridged by the raised portion 33 of the stiffening plate. A hook 31 on the portion 33, and preferably integral therewith, may be used for manipulating the follower 33 and for catching the follower to one of the handles of the plunger assembly, as illustrated in dotted lines in Fig. 1, thus suspending the follower when it is desired to have the pressure of the follower removed for any purpose, such as the insertion of new staples. The strip of spring steel 33, which is coiled to form the actuating memberof the feeder device indicated at 3| in Fig. 1, has its end riveted at 33 to the portion 33 of the stifl'ening plate. The top of the rib 22 may be grooved to receive the lower end of the rivet 33 if necessary.

The feeder spring device 3i comprises the coil spring 33, the outer end of which is riveted to the follower 33 and the inner end of which is fixed in a spring clip 32. This spring clip has a curved tongue 33 for supporting the beginning of the inner coil of the spring so as to avoid so short a bend of the spring strip as to bring about a fracture at this point. The end of the strip 33 may be secured in the clip 32 at 33 in any suitable fashion, it being possible to rivet the strip to the clip, or to deform the clip so as to clamp the end of the spring strip. The clip itself has lateral lugs 33 down-turned at the ends. These lugs are receivable in slots 33 in a yoke 31 which then may be secured by screws 33 to the lower portion of the plunger housing 3 closely adjacent the base assembly. The-screws 33 secure the yoke 31 to 'up-turned lugs 33 of the bed-plate 3 by passing through out-turned cars 33 on the end of the yoke opposite the slots 33. Accordingly, the feeder spring device is principally received within the plunger housing 3, and the strip 33 is' effective for drawing the follower 33 close up to the plunger. This means that even though the follower 33 is relatively short (cutting down the capacity of the feeding means 3 but little), it can be drawn by the coil spring to a position closely adjacent the plunger soas to complete feeding of the staples. I

The plunger housing 3 is shaped to receive the plunger 32 and guide the same as it reciprocates toward and from the work. The plunger is adapted to cooperate with relatively wide staples, and to shear a staple from the end of a strip of staples by cooperation with the cutter bar 23. Accordingly, the plunger proper takes the form of a metal plate 33 having a cutting edge 33. The plunger furthermore carries spring housings 33 which, as illustrated herein, are formed integral with the plate 33. The parts 33 and 33 maybe formed from a single plate by bending marginal portions of this plate into the shape of the spring housings 33. housed therein and abut against upper rests 33 and lower stools 33. The upper rests 33 project through slots 33 in the plate 33 and engage in openings 3i (see Fig. 9) in the plunger housing 3. Lugs 33 project from the other side of the spring rests 33 through slots 33 in the housings 33 and through openings 33 in the plunger housing 3., The spring rests 33, as thus extended at opposite in Fig. 7, however, the rest 331s shown pushed by.

the spring 33 clear to the ends of these slots because the plunger 32 is removed from the hous ing 3. The lower stools have forwardly and rearwardly projecting lugs 33 received in slots 33 in the housings 33. These rests 33 also have downs wardly projecting feet or lugs I3 which extend slightly below the bottoms of the housings 33 when the lugs 33 are at the bottoms of the slots 33.

It will be understood from the above description of the plunger 32 that there are no stops against which it strikes solidly. In operation the plunger is retracted away from the work and then released, in a manner later to be described; and the compression springs 33 are compressed during the retraction of the plunger and are thereupon effective upon release of the plunger to actuate the same toward the work, the springs 33 being recompressed as the plunger nears the end of its stroke toward the work to cushion the stroke. The slots 33 and 33 should be long enough so that as the plunger 32 is raised relative to the housing 3, the housings 33 may move upwardly relative to the rests 33 which are engaged in the openings 3i and 33 in the housing 3. The slots 33 need he of but. small extent, as the stools 33 en a e the bottoms of these slots during retraction of the plunger away from the work, and there is movement of the lugs 33 in the slots 33 only when the feet 13 strike against the bed plate 3 toward the end of the stroke of theplu-nger 32 to cushion the same. The extent of movement of the plunger 32 after the lugs 13 strike the base plate 3 is but small, so that the lugs 13 need to extend but slightly below the bottoms of the housings 33. The stools 33 are not in engagement with the ends of the slots 33 when the spring rests 33 are in engagement with the ends of the slots 33 and 33 if the plunger 32 be assembled in operative rela- Coil compression springs 33 are tion with the housing 5; in Fig. 7, however. the plunger 52 is removed from' the housing I, and the rests and stools are free to move to the limit allowed by the respective slots.

when the feet or lugs II of the rests or stools 5s strike the bed plate 5, the ends of the springs 56 which rest on these stools, are stopped in their downward motion and therefore cease to urge the plunger 52 in its driving stroke. Fig. 7 illustrates the positions of the rests 58 and I! in the plunger at this point. However, due to its momentum, the plunger continues in its downward movement, resulting in engagement by the upper rests 58 with the upper ends of the slots I and in the plunger 52 so as to carry said rests 5| downward as shown in Fig. 17. These rests 5. function to compress the springs as the plunger is retracted and also act against the upper ends of the springs 55 at the end of the driving stroke recompressing said springs 56 so as to cushion said plunger. When the force of the driving stroke has become completely exhausted, the springs 56 expand until the upper rests 58 have moved upward approximately into contact with the ends of the slots 66 and Si in the housing 5.

The above description has been applied to the plunger 52, illustrated in detail in Fig. 3, which is particularly adapted for driving wide staples. It is clear that this same principle of cushioning the stroke of the plunger may be applied to mechanism for driving narrow staples such as illustrated in Figs. 6 and 19. In such staple driving mechanism, a narrow plunger will be employed,

and but one spring 56 and but one housing 55 will be required. The upper rest 58 and lower stool 59 will operate in precisely the same manner in the mechanism shown in Fig. 6 as in the wide mechanism. The cushioning of the stroke of the plunger has long been a troublesome problem in staple driving mechanisms of this type. Not only does the double use of the driving spring 56 bring about cushioning in an effective manner, but it also considerably simplifies the mechanisms in the plunger assembly.

The use of a pair of springs in mechanism for driving wide staples balances the forces exerted on the plunger. It moreover provides the necessary driving force without necessitating the use of one relatively stifi powerful spring. Moreover, the space between the housings 55 accommodates the feeder spring device 3i so that the latter is positioned closely adjacent the plate 53, thus lengthening the extent of inward travel of the follower 30.

The plunger is, in accordance with my invention, retracted away from the work by a lever 15 such as shown in Fig. 1. For convenience in gripping, a stationary handle 16 is fixed at 11 to an extension 18 of the plunger housing 5. The follower 30 when withdrawn from the guide channel 20 may be hooked to the outer end of the handle 16 as indicated in dotted lines in Fig. 1. The lever 15 has a hardened nose for cooperating with a cross-bar Bl fixed between the housings 55. When the nose 80 slips out from under the cross-bar 8i, the plunger 52 is released to be driven by the compression springs 56 against the staple which has been moved by the feeding means 4 over the cutter bar 25 into operative position beneath the plunger. The stroke of the plunger drives the staple ahead of the lower edge of the plate 53 into the work. The depending ends of the staple are at this time guided by the lugs 25 (see Fig. 9) extending downwardly from the bed plate 6 and preferably formed integral therewith. As the bed plate is of heavier metal than the housing l.=this provides a rugged construction for guiding the plunger and staple as the latter is driven into the work. I

The lever 15 may, if desired. be provided with a trigger of any suitable type such ask now customarily used, this trigger-to replace the integral nose I. shown in Fig. 1. I prefer, however, to employ the construction shown in Fig. 1 in which the conventional trigger mechanismis replaced by a pivot on which the lever 15 is slidably mounted. This pivot arrangement permits movement of the lever away from and toward the plunger 52, thus providing for release of the crossbar II and for later re-engagement of the nose ll beneath this cross-bar. In the form of slidable pivot illustrated in Fig. 1 a pin 05 is fixed in the extension 18, and a second pin or abutment is mounted in the extension 18 below the pin 85. The pin 85 extends through a slot 81 in the lever 15, and when a heel 88 on the lower side of the lever I5 engages the pin or abutment 88, the slidable pivot mounting afforded by these parts permits lever I5 to move away from the plunger to withdraw the nose 8|! from beneath the cross-bar 8|.

Instead of having a fixed abutment such as the pin 86, I may employ an abutment which is adjustable toward and away from the plunger, a set screw or a pair of set screws being adapted to this purpose. Fig. 18 illustrates such a construction, parts corresponding to the parts shown in Fig. 1 being given the same reference numeral. A set screw 86a is shown as engaging the abutment 85b for varying the position in which the latter engages the heel 88 for causing the lever 15 with its slot 81 to slide on the pin 85. In such case, the set screw or set screws may be adjusted inwardly or outwardly to vary the time at which the nose 8!! pulls out from under the crossbar 8i, thusvarying the extent of upward stroke, and accordingly the force with which the staple is driven into the work.

As the lever 15 is swung in the opposite direction to re-engage the nose 80 beneath the crossbar 8i, the end of the lever slides on the crossbar ill to cause the lever to remain away from the plunger until the nose '8!) has cleared the crossbar 8i, when the nose 80 may again engage beneath the cross-bar 8i. A spring 90 twisted about the pins 85 and 86 is efiective for automatically returning the lever 15 to the position shown in Fig. 1. One end of this spring is passed through an opening Si in the inner portion of the lever and the other end engages beneath the lever at 92. This spring 90 presses the lever toward the plunger, thus tending to keep the nose 8!! engaged beneath the cross-bar 8i. Moreover, the spring 90 tends to turn the lever'15 in a counterclockwise direction. When the plunger 52 has been retracted and then released, the lever 15 may be let go and the spring 90 will thereupon turn the lever 15 in a counterclockwise direction. The slot 8'! permits the lever to move away from the plunger far enough for the nose 80 to pass the cross-bar 8|, whereupon the spring 90 pushes the lever 15 toward the plunger to re-engage the nose 80 beneath the cross-bar 8i.

While certain advantages of my improved staple driving mechanism have been discussed in the course of the above description, other advantages will be readily apparent to those skilled in the art. I have illustrated and described the embodiment of my invention which I at present prefer, but it will be understood that the invention may be otherwise embodied and practiced within the scope of the following claims.

I claim:

l. A staple driving mechanism comprising a plunger, mechanism for retracting the plunger away from the work and releasing the same for a staple driving stroke, a compression spring, and means acting on the opposite ends of the spring for compressing said spring during the retracting stroke of the plunger and for assisting in stopping the driving stroke of the plunger by recompressing said spring so as to cushion said stroke, said. means connecting said spring and plunger for opposing said spring in such cushioning to further movement of the plunger.

2. A staple driving mechanism comprising a plunger, mechanism for retracting the plunger away from the work and releasing the same for a staple driving stroke, a compression spring, and rests at the opposite ends of the spring acting on the spring for compressing the same, one of said rests having a lost motion connection with the plunger and having a projection hitting just prior to the end of said driving stroke to stop further movement of said rest, the rest at the opposite end of the spring being engaged by the plunger substantially simultaneously therewith,

said rest opposing the spring to further movement of the plunger.

3. A staple driving mechanism comprising a plunger, mechanism for retracting the plunger away from the work and releasing the same for a staple driving stroke, a compression spring, and means for cushioning the driving stroke of the plunger comprising a rest engageable with the striking end of the spring, and means engageable with said rest Just prior to the end of said driving stroke to stop further movement of said rest and oppose the spring to further movement of the plunger.

4. A staple driving mechanism comprising a housing, a plunger reciprocable therein, mechanism for retracting the plunger away from the work and releasing the same, and resilient means for driving the plunger toward the work and for cushioning such stroke of the plunger, said resilient means comprising a spring storing energy during the retracting stroke of the plunger and actuating the plunger during the driving stroke thereof, and means connecting said spring to the plunger and housing for cushioning the driving stroke of the plunger by opposing said spring to further movement of the plunger.

5. A staple driving mechanism comprising a plunger, means for retracting the plunger away from the work and releasing the same, and resilient means for driving the plunger toward the work and for cushioning such stroke of the plunger, said resilient means comprising a compression spring acting through one of its ends for biasing said plunger toward the work and a rest for the other end of said compression spring engageable by the plunger adjacent the end of said driving stroke for cushioning the plunger.

6. A staple driving mechanism comprising a housing, a plunger reciprocable therein, mechanism for retracting the plunger away from the work and releasing the same, and resilient means for driving the plunger toward the work and for cushioning such stroke of the plunger, said resilient means comprising a compression spring and rests at the opposite ends of the spring, each rest having limited movement relative to both the plunger and the housing, one rest moving with the plunger during the retraction and driving strokes of the plunger and remaining stationary with the housing during the cushioning of the plunger.

7, A staple driving mechanism comprising a staple guide. 'a relatively wide plunger reciprocable transversely relative to the guide, means for retracting the plunger away'from the work and releasing the same, and a plurality of compression springs for actuating the plunger toward the work, said plunger providing housings integral therewith for enclosing the actuating springs.

8. A staple driving mechanism comprising a plunger, means for biasing the plunger toward the work, a lever for retracting the plunger away from the work and releasing the same, and means for so shiftably fulcruming the lever as to permit reengagement of the lever with the plunger by movement of the lever away from and toward the plunger.

9. A staple driving mechanism comprising a plunger, means for biasing the plunger toward the work, a lever for retracting the plunger away from the work and releasing-the same, a shiftable fulcrum for the lever permitting the lever to move bodily toward and away from the plunger, and a spring for urging the lever toward the plunger.

10. A staple driving mechanism comprising a plunger, means for biasing the plunger toward the work, a lever for. retracting the plunger away from the work and releasing the same, means providing' a fulcrum for said lever which affords relatlve bodily movement between the lever and its fulcrum permitting movement of the lever toward and away from the plunger, and an abutment engageable by thelever in turning on its pivot for displacing said lever relative to the plunger.

11. A staple driving mechanism comprising a plunger, resilient means for urging the plunger toward the work, a lever for retracting the plunger away from the work and releasing the same,

said lever having a slot therein, and means cooperating with the slot for so fulcruming the lever that the lever is shii'table bodily toward and. away from the plunger, and a spring for biasing the lever toward the plunger.

12-. A staple driving mechanism comprising a plunger, aspring for urging the plunger toward the work, a lever for retracting the plunger away from the work, a pin cooperating with a slot in the lever to support the latter for bodily movement toward and away from the plunger, an

abutment engageable by the lever in turning on its pivot for displacing said lever away from the plunger, and a spring biasing the lever in the opposite direction about its pivot and toward the plunger.

13. In a staple driving mechanism including a staple guide having a longitudinal rib, a follower for advancing staples along said guide, said follower comprising a channel shaped body member and a stiffening plate secured thereto and having a raised portion bridging, the longitudinal rib of the staple guide, the body member having a recess receiving the raised portion of the stiilening plate.

14. In a staple driving mechanism including a staple guide, a follower for advancing staples along said guide, said follower comprising a channel shaped body member having an opening in the web of the channel and a stiffening plate secured within the channel to the web thereof, said stiifening plate having a raised portion received within said opening.

15. In staple driving mechanism, staple feeding means comprising a staple guide having upturned flanges and an intermediate longitudinal rib, said flanges and rib cooperating to support the staples, and a follower for advancing staples along the guide, said follower comprising a channel shaped body member stiffened by a plate secured to the under side of the web of the channel, said web having a recess receiving a portion of the stiffening plate for clearing said rib.

16. In staple driving mechanism, staple feeding means comprising a housing, a staple guide therein having upturned lateral flanges and an intermediate longitudinal rib, said flanges and rib cooperating to support the staples, and a follower for advancing staples along the guide within the housing, said follower comprising a body member channel-shapedin cross-section to overlie the guide with its flanges depending between the flanges of the guide and said housing, and a stiffening plate secured'to the underside of the web of the channel, said web having a recessreceiving a portion of the stiffening plate for clearing said rib.

17. A staple driving mechanism comprising a plunger, means for biasing the plunger toward the work, a lever for retracting the plunger away from the work and releasing the same, a shiftable fulcrum for the lever permitting the lever to move bodily toward and away from the plunger, said lever having a portion on one side of its fulcrum for ermagement by the operator's hand and a plunger-engaging portion on the other side of its fulcrum, and means engageable by the lever in turning on its pivot for causing outward movement of the lever away from the plunger'to release the latter. I

" 18. A staple driving mechanism comprising a plunger, means for biasing the plunger toward the work, a trip lever for retracting the plunger away from the work and releasing the same, means cooperating with said lever for pivotally mounting the lever and permitting the same to shift to release the plunger, said means comprising a pin and slot connection permitting bodily shifting of the lever toward and away from the plunger, and an adjustable abutment engageable by the lever in turning on its pivot for determining the point of release of the plunger from said trip lever.

19. In a staple driving mechanism including a staple guide and a housing therefor having flanges for overlaying staples on the guide, a follower for advancing staples along said guide, said follower comprising a body member movable along the guide with its outer portions beneath said housing flanges, and a stiffening plate underlying said body member and extending adjacent to said flanges of the housing.

20. In a staple driving mechanism including a staple guide having up-turned lateral flanges and a housing for the guide having flanges for overlying the staples moved along the guide, a follower for advancing staples along said guide, said follower comprising a channel-shaped body member, and a stiffening plate underlying the same and extending to abut said up-turned lateral flanges.

21. In staple driving mechanism, staple feeding means comprising a sheet metal staple guide having upturned lateral flanges and an intermediate longitudinal rib, cooperating with said lateral flanges to support the staples, and a follower for advancing staples along the guide.

22. In a staple driving mechanism in combination, a plunger assembly including a plunger and a plunger housing, and means for feeding staples beneath the plunger including a staple guide, a

follower cooperating therewith, a demountable yoke mounted on the plunger housing, a spring clip, a coil spring carried by said clip and operatively connected to said follower, the ends of said clip projecting from the coil spring, said yoke having slots receiving the ends of the clip by sliding movement in the direction of tension of the spring.

23. A staple driving mechanism comprising a plunger housing, a plunger reciprocable therein, said plunger including a relatively wide blade for engaging the staples to drive the same intov the work and spaced spring housings integralwith the plunger, means for retracting the plunger away from the work and releasing the same, compression springs in said housings, and rests for the springs acting to compress the same during the retracting of the plunger.

24. In a staple driving mechanism, a plunger stamped out of sheet metal and including a relatively wide blade with the side portions bent into enclosures adapted to house driving springs for the plunger.

25. A staple driving mechanism comprising a plunger, mechanism for retracting the plunger away from the work and releasing the same fora staple driving stroke, a compression spring, and means including rests acting on the opposite ends of the spring for compressing said spring during the retracting stroke of the plunger and for assisting in stopping the driving stroke of the plunger by recompressing the spring so as to cushion said stroke. one of said restshaving a lost motion connection with the plunger and having a projection hitting just prior to the end of said driving stroke to stop further movement of said rest.

J. SPENCER. 

